The present invention relates generally to the field of optics and in particular to an interferometric system for birefringence characterization of one or more samples.
Precise characterization of static or dynamic material birefringence is important and useful in applications that range from testing of optical components to measuring the viability and function of biologic tissue. While there are techniques that measure linear birefringence of samples, there remains a need for improved resolution and characterization, especially for samples or materials that are highly transparent, turbid and/or highly scattered. For example, fiber-based optical low-coherence reflectometery (OLCR) systems have been found to be rugged, relatively alignment-free, may be integrated with other sensing platforms and are flexible in interrogating a variety of samples. Unfortunately, fiber implementation of a polarization-sensitive OLCR system with standard single mode fiber is complicated since polarization state in a single mode fiber randomly fluctuates due to microscopic defects in the fiber, core ellipticity and external environmental perturbations. In addition, non-polarization maintaining (PM) fiber-based polarization-sensitive OLCR systems that perform birefringence characterization, work with multiple measurements and with different input polarization states to overcome the problem of fluctuating polarization state of light incident on the sample. Non-PM fiber-based setups cannot reliably measure birefringence of a sample with a single measurement even when using short lengths of fiber in the interferometer.
A technique that appears to be of more benefit for characterizing the birefringence of a sample is the polarization-sensitive optical low-coherence reflectometery (PS-OLCR). PS-OLCR is extremely useful for depth resolved birefringence characterization of transparent and highly scattering samples. With this technique, polarization maintaining single mode fibers can be used to construct a polarization-sensitive OLCR system, because the orthogonal polarization modes are isolated and preserve the input polarization state. Multiple measurements for birefringence characterization, however, limit detection of fast transient birefringence changes in a sample and are subject to any motion related artifact between multiple acquisitions. Although PM fiber based polarization-sensitive OCLR have been proposed to solve such problems, functioning and working systems have not been adequately constructed. Another disadvantage of current PM-OLCR systems is that they use bulk interferometric setups to interrogate samples for birefringence measurement. Therefore, there remains a need for a proper and efficient functioning PM-OLCR system useful for accurate birefringence characterization of a sample.